The Ba/Ca record of corals from the Southern Gulf of Mexico: Contributions from land-use changes, fluvial discharge and oil-drilling muds

The Ba/Ca in the growth bands of Montastraea faveolata from the Veracruz Reef System was used to reconstruct the long-term environmental change associated to anthropogenic activity in the Southern Gulf of Mexico (SGM). The 168-yr coral record shows two periods of distinct Ba concentrations: a pre-industrial period (1835-1965: 7.54 μmol/mol) followed by an industrial one (1966-2000: 8.57 μmol/mol). As human population quadrupoled during the latter, sediment load in the fluvial discharge also increased due to changes in land-use, yielding a 14% increase in the Ba-levels. A remarkable finding is that the periods at which the coral Ba/Ca ratio losses its correlation with fluvial discharge coincide exactly with peak periods of high barite consumption (used for oil drilling) in the Northern Gulf of Mexico, and the onset of oil drilling in the SGM. This finding suggests that barite may be one of the dominant sources for dissolved-Ba in the SGM.     

Precision abundance analysis of bright H ii galaxies

We present high signal-to-noise ratio spectrophotometric observations of seven luminous H  ii galaxies. The observations have been made with the use of a double-arm spectrograph which provides spectra with a wide wavelength coverage, from 3400 to 10 400 Å free of second-order effects, of exactly the same region as that of a given galaxy. These observations are analysed applying a methodology designed to obtain accurate elemental abundances of oxygen, sulphur, nitrogen, neon, argon and iron in the ionized gas. Four electron temperatures and one electron density are derived from the observed forbidden line ratios using the five-level atom approximation. For our best objects, errors of 1 per cent in t _e([O  iii ]), 3 per cent in t _e([O  ii ]) and 5 per cent in t _e([S  iii ]) are achieved with a resulting accuracy of 7 per cent in total oxygen abundances, O/H.
The ionization structure of the nebulae can be mapped by the theoretical oxygen and sulphur ionic ratios, on the one side, and the corresponding observed emission line ratios, on the other – the η and η' plots. The combination of both is shown to provide a means to test photoionization model sequences presently applied to derive elemental abundances in H  ii galaxies.     

Quantifying atmospheric stability conditions at a swine facility and an adjacent corn field in Iowa, USA

Atmospheric stability conditions in the atmospheric surface layer control the distance and direction of transport of air contaminants. Near confined animal facilities, transport processes significantly impact air quality as these sites typically act as point sources of dust and odor constituents; however, little information is available on atmospheric stability effects. This study was conducted to assess year-round temporal patterns of atmospheric stability at a swine production facility and an adjacent commercial corn field (CF) in the US Midwest. Two towers of 10 and 20?m heights for continuous micrometeorological measurements were deployed within a CF and between swine buildings (BSB), respectively. Each tower was equipped with an eddy-covariance system at 6.8?m height, infrared thermometers, and six cup anemometers with thermocouples installed at log-distributed heights. Overall results from gradient Richardson number and Monin?CObukhov (z/L) calculations revealed a greater prevalence of unstable conditions for BSB compared with CF. During the 13-month measurement period, unstable cases (z/L ranging from ?1 to ?0.01) occurred 1.4 times more frequently for BSB than CF (52 vs. 39%, respectively), while stable cases (0.011?C0.2) were 1.8 times more frequent for CF than BSB (24 vs. 14%, respectively). These patterns were partly associated with higher surface radiometric temperatures for BSB. Relatively greater diurnal heat capture at BSB (ground and roof surfaces) and a cooling effect in CF through active canopy transpiration during the daytime explain these z/L and radiometric temperature results. Prevalent diurnal atmospheric instability at BSB suggests enhanced ascendant vertical transport of air pollutants perhaps causing greater mixing/dilution with the atmospheric layer and/or their facilitated transport over greater distances when sorbed onto particles. This enhanced understanding of the spatio-temporal patterns of atmospheric stability can be subsequently applied in further studies for identifying effective odor mitigation strategies near commercial animal production facilities.     

Energy balance and turbulent flux partitioning in a corn–soybean rotation in the Midwestern US

Quantifying the energy balance above plant canopies is critical for better understanding of water balance and changes in regional weather patterns. This study examined temporal variations of energy balance terms for contrasting canopies [corn (Zea mays L.) and soybean (Glycine max L. Merr.)]. We monitored energy balance for 4 years using eddy-covariance systems, net radiometers, and soil heat flux plates in adjacent production fields near Ames, Iowa. On an annual basis, soybean exhibited 20% and 30% lower sensible heat flux (H) and Bowen ratio than corn, respectively. As canopies developed, a gradual shift in turbulent fluxes occurred with decreasing H and increasing latent heat flux (LE), but with a more pronounced effect for corn. Conversely, during mid-growing season and as both canopies progressively senesced, H in general increased and LE decreased; however, soybean exhibited slightly greater LE and much lower H than corn. These temporal variations in magnitude and partitioning of turbulent fluxes translated into a pronounced energy imbalance for soybean (0.80) and an enhanced closure for corn (0.98) in August and September. These discrepancies could be directly associated with differences in momentum transport as shown by friction velocities of 0.34 and 0.28 m s^?1 for corn and soybean, respectively. These results support influential roles of plant canopy on intensity and mode of surface energy exchange processes.     

Verification of a Synthesized Method for the Calculation of Low-Level Climatological Wind Fields Using a Mesoscale Boundary-Layer Model

Low-level climatological wind fields over the La Plata River region of South America are synthesized with a dry, hydrostatic mesoscale boundary-layer numerical model. The model is forced at the upper boundary with the 1200 UTC local radiosonde observations and at the lower boundary with a land-river differential heating function defined from the daily meteorological observations of the region. The climatological wind field is defined as the mean value of a series of individual daily forecasts, employing two methods. The simplified method considers a 192-member ensemble (16 wind directions and 12 wind-speed classes at the upper boundary). Each member has a probability of occurrence that is determined from the 1959–1984 observations; the daily method uses a total of 3,248 days with available data during the same period. In both methods each realization is a daily forecast from which the mean wind distributions at 0300, 0900, 1500 and 2100 local standard time are calculated and compared to the observations of five meteorological stations in the region. The validation of the climatological wind fields for both methods is evaluated by means of the root-mean-square error of the wind-direction frequency distribution and mean wind speed by wind sector. The results obtained with the two methods are similar, and the errors in wind speed are always smaller than those in wind direction. The combined errors of wind direction and wind speed show that the ensemble method is outperformed by the daily method, on average by meteorological station in only one out of five of them, and on average by the time of the day in only one out of 4 h. The conclusion of the study is that the ensemble method is an appropriate methodology for determining high resolution, low-level climatological wind fields, with the boundary-layer model applied to a region with a strong diurnal cycle of surface thermal contrast. The proposed methodology is of particular utility for synthesizing wind fields over regions with limited meteorological observations, since the 192-member matrix can be easily defined with few observing points, as well as in the case of relatively incomplete records.     

Contribution to the knowledge of the Domeyko Range in the Andes of Northern Chile

This work describes a geological scheme of the pre- And ean Domeyko Range of Northern Chile. This pre- And ean area consists of a basement formed by Paleozoic granitic, volcanic, and marine sedimentary rocks, and by Triassic acidic volcanics with continental intercalations. The Andean Basin developed in the Lias over the basement, with initial stages that include volcanic and continental sequences. A continuous marine environment existed in the Hettangian-Tithonian span, with volcanic events in the Bajocian, Callovian, Kimmeridgian, and Tithonian. Evaporitic facies developed in the Oxfordian-Kirnmeridgian. A marine-continental basin is recognized in the Neocomian, the Upper Cretaceous being represented by volcanic and continental deposits, a development similar to the Tertiary one; over these sequences volcanic, detrital, and saline deposits were laid down in the Plio-Pleistocene. Compressional tectonic cycles developed in the Upper Paleozoic, Upper Lias?, Upper Jurassic, Upper Cretaceous, and Tertiary, and tensional phases occured in the Triassic, Cretaceous, and Tertiary. The compressional stages were characterized by intrusive cycles while the tensional phases witnessed volcanic sedimentary events.     

Pressure and density gradients in H II Regions

Here we discuss the effects of large ambient pressures and decreasing density gradients on the observed properties of dusty UC hii regions. Dust absorption can effectively reduce the size of the photo ionized region, and density gradients can modify the spectral index of the emission. The effects of the density gradients seem to be present in both galactic and extragalactic HII regions.